[OKDXA] The weak spot in my dipole

Fri Jul 1 12:26:47 EDT 2016

Think PolyPhaser, accept no substitutes! 

-----Original Message-----
From: OKDXA [mailto:okdxa-bounces at mailman.qth.net] On Behalf Of John Geiger
Sent: Friday, July 01, 2016 10:07 AM
To: Oklahoma DX Association
Subject: Re: [OKDXA] The weak spot in my dipole

Thanks for the suggestions-PROBLEM SOLVED!

I borrowed another manual tuner and a dummy load from a friend.  The antenna was doing the same
thing with the other tuner, so that eliminated the tuner, which would have been the most expensive
part of the system to replace.  My next plan was to unhook the coax from the balun and hook it to
the dummy load, so see if the coax was ok.  While getting ready to do that, I noticed one part of
the system I forgot to mention-the lightning arrestor.  It is one of those cheap ones that has a
PL239 on 1 end and a
SO239 on the other, with a screw you attach the ground wire to, and it is supposed to bleed static
off of the antenna.

Obviously the lightning arrestor wasn't sealed very well, because when I removed it, the SO239 part
of it was rusty.  I found some sandpaper, sanded the corrosion off of the PL259 on the end of the
coax, threw away the lightning arrestor, hooked the coax up to the balun, and everything is working
fine now!  Made a few 40m QSOs in the Canada Day contest with no problems.

When telling this to the XYL, she agreed that maybe next time I get a lightning arrestor, I
shouldn't get one for $5 off of ebay.

John AF5CC

On Thu, Jun 30, 2016 at 9:32 PM, Perry Jenkins via OKDXA < okdxa at mailman.qth.net> wrote:

> Check your coax with a megaphmmeter. Disconnect from the antenna and test.
> This tests  for breakdown in the dialectic of coax at high voltage. 
> This can find defects that don't show up with continuity checks with a 
> standard VOM.
>
> Perry N5PJ
>
> Sent from my iPhone
>
> > On Jun 30, 2016, at 14:22, John Geiger <af5cc2 at gmail.com> wrote:
> >
> > spot" in my dipole
> > <
> http://www.eham.net/ehamforum/smf/index.php/topic,110022.msg935431.htm
> l#msg935431
> >
> > < *on:* *Today* at 11:45:32 AM >
> > [image: Reply with quote]*Quote*
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> 022.0;msg=935431;sesc=5c1acd5339f71a99ad263040698a5c0e
> >
> > ------------------------------
> > I have a homebrew G5RV type dipole that I made around 18 years ago.
> > Overall it has been a very good antenna for me and I have worked 
> > lots of
> DX
> > with it.  It is around 100 feet of copper wire, joined to a run of 
> > 300ohm Radio Shack twin lead, maybe 25 feet or so.  At the twin lead 
> > to coax junction I have a Unidilla 4:1 Voltage Balun, and then 20 
> > feet of RG11 75ohm coax.
> >
> > A couple of years ago I was using a MFJ 918 1:1 current balun, and 
> > on
> some
> > of the lower bands, I couldn't keep the antenna "tuned".  I am using 
> > a
> MFJ
> > 941D tuner, and I would tune the antenna tuner on 40 or 80 for the 
> > lowest SWR, and once I started transmitting the SWR would jump up to 
> > infinity,
> so
> > I would transmit a carrier, retune it, and once I transmitted again, 
> > same problem, the SWR would jump up.  A few months ago I replace the 
> > MFJ balun with the Unidilla 4:1 Voltage Balun because when I 
> > originally built the antenna, I had a Van Gordon 4:1 voltage balun, and it worked fine.
> >
> > Changing baluns seemed to fix it for a while, but now I am having 
> > the tuning problem again, but it happening on all bands, not just 40 and 80.
> > Luckily I have a miniquad for the higher bands, but I tried the 
> > dipole on 20 and 17 today with the same losing tune problem.
> >
> > Before I go climbing around on the roof changing stuff out, does 
> > anyone have an idea of where to start-what might be causing this tuning problem.
> > Same thing as before, I would load up the dipole to a 1:1 SWR, using 
> > a
> less
> > than 100 watt carrier, but once I go and start transmitting at full 
> > power the SWR quickly jumps way up.  I go retune it,which just 
> > requires a
> slight
> > adjustment, and the SWR jumps up again, and it just keeps doing 
> > this.  I don't think it is the MFJ tuner because it doesn't have 
> > this problem with the miniquad, which also goes through the tuner.
> >
> > Also, the dipole shows a low SWR (2:1 or less) on 12 and 15 meters, 
> > and when I put the tuner in bypass mode I can transmit on the dipole 
> > with no problems with losing its tuning.  On 80m the SWR is also 
> > low, and transmitting on bypass mode to the dipole usually works but 
> > once in a
> while
> > it will its tuning.  On 30m it will show a low SWR initially but 
> > once I start transmitting (in bypass again) the SWR quickly goes to infinity.
> On
> > 40m when I tune the antenna and then transmit at 10 watts it seems 
> > to
> stay
> > tuned.  Going up to 25 watts detuned it again.
> >
> > So, any ideas or guesses as to where the problem in my system is?
> >
> > 73 John AF5CC
> > Report to moderator
> > <
> http://www.eham.net/ehamforum/smf/index.php?action=reporttm;topic=1100
> 22.0;msg=935431
> >
> >    199.96.203.51
> > <
> http://www.eham.net/ehamforum/smf/index.php?action=helpadmin;help=see_
> member_ip
> >
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